The work to be conducted during the next year involves three approaches to donor pre-treatment prior to allotransplantation. Preliminary work has been performed in each of these areas during the past year. I. Cytotoxic Agents: the effectiveness of donor animal pretreatment prior to cardiac heterotopic transplantation with antilymphocyte globulin (ALG) alone and in combination with cyclophosphamide (CY) will be evaluated. The data obtained will be compared with our results of CY pretreatment alone at 6, 18, 24, and 48 hours prior to transplantation. II. Isolated donor organ perfusion: a series of isolated heart perfusions with modified Krebs-Henseleit buffer for one, two and three hours prior to transplantation will be completed and compared with similar perfusion protocols in hearts removed from CY pretreated animals. Isolated heart perfusion with ALG in Krebs solution will be performed at varying temperatures and for various intervals prior to allotransplantation. Isolated heart perfusion will be performed for varying intervals followed by donor organ perfusion with recipient blood in an attempt to repopulate the graft wiih recipient passenger leukocytes prior to transplantation. III. Selective lymphatic ablation with radioactive substances: 109Pd-Porphyrin complexes will be injected into donor animals, donor and recipient animals and recipients alone in an attempt to selectively ablate lymphatic tissue and therefore prolong allograft survival.